1. Field of the Invention
The present invention relates to an ionization apparatus for a solid sample, a mass spectrometer including the ionization apparatus, and an image forming system.
2. Description of the Related Art
There is a technology for ionizing a solid under the atmospheric pressure condition for component analysis of a surface of a solid sample.
In the document Yoichi Otsuka et al., “Scanning probe electrospray ionization for ambient mass spectrometry”, Rapid Communications in mass spectrometry, 26, 2725 (2012), there is proposed an ionization method in which a very small volume of solvent is supplied to a very small region on a solid sample surface so that components of the sample are dissolved in the solvent, and then the components are ionized by an electrospray ionization method. The generated ions are introduced to a mass spectrometer so that a mass-to-charge ratio of the ion is measured, and hence the component analysis can be performed. In order to supply the solvent to the very small region of the solid sample surface, a probe is used. The solvent is continuously introduced to the probe. In a state where the probe is close to the solid sample surface, a liquid bridge is formed between the probe and the solid sample surface so that the components of the solid sample surface are dissolved in the liquid bridge. The solution in which the components are dissolved is ionized by applying a voltage thereto. The ionization method performed in the state where the probe stays close to the solid sample surface is referred to as contact-mode scanning probe electrospray ionization (contact-mode SPESI), and the ionization method performed in the state where the probe is vibrated so that the solvent is intermittently supplied to the solid sample surface is referred to as tapping-mode scanning probe electrospray ionization (tapping-mode SPESI).
In the above document, the probe is vibrated so that the probe is intermittently brought into contact with the sample surface, and hence the liquid bridge is intermittently formed. Therefore, a time period for forming the liquid bridge and a time period for ionizing are defined by a vibration condition of the probe such as vibration frequency, and hence cannot be determined freely. Therefore, depending on a condition such as the probe vibration or a solution flow rate, there is a problem in that when the components are consecutively measured by scanning the sample surface, sample components dissolved in the liquid bridge at a certain measurement point on the sample surface remain in another liquid bridge formed at a next measurement point, and hence the dissolved components at both measurement points cannot be analyzed correctly and separately.